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243 million years ago, our planet was arid, the poles were tropical, and the continents were lumped together in one great mass. Turtles, ants and crocodiles all walked the Earth. But one thing scientists weren’t sure of was whether dinosaurs had yet appeared on the scene.

Now, however, those doubts have been put to rest thanks to the discovery of what may be the world’s oldest dinosaur bones. The remains of the Nyasasaurus parringtoni, a labroador-sized creature with a 5-foot tail, are 10 to 15 million years older than any other dinosaur fossils found thus far.

The findings could help resolve 150 years of debate about when dinosaurs arrived on Earth. Until now, the only signs scientists have been able to find of dinosaurs during this period, the Middle Triassic, were fossilized footprints and the occasional ambiguous bone, which might have belonged to a reptile. Thanks to this 135-pound dino (or rather, its upper arm bone and vertebrae), they now know that dinosaurs (or at least animals very much like them) were indeed around at that time.

Based on the bones, scientists guess that the creature stood upright, was about three feet tall, seven to 10 feet long, and weighed between 45 and 135 pounds. How do they know it’s part of the same family that gave us the raptor and T-rex? The bone fibers in N. parringtoni‘s humerus show the haphazard fiber development characteristic of dinos, which evolved to grow really, really fast.

The bones were originally pulled from land that now forms part of Tanzania back in the 1930s. But the specimens, which come from two different animals and are housed in London and Cape Town museums, were never studied in detail until now. “80 years later, we’re putting it all together,” says Sterling Nesbit, lead author on the paper and a postdoctoral researcher at the University of Washington. The location of the bones suggests that dinosaurs emerged from the south of the great supercontinent Pangaea.

The discovery puts to rest the notion that dinosaurs burst onto the scene during the Late Triassic and then spread at lightning speed. Turns out dinosaurs are just like everybody else, emerging slowly as part of a group of animals called archosaurs, which includes crocodiles. Back in the Triassic, life on earth was recovering from the Permian extinction, or the “Great Dying” which wiped out most of the species on the planet. At the time, the air hardly contained any oxygen and ocean temperatures rose to 104 degrees Fahrenheit. After the great extinction, life slowly recovered, and it was under these conditions that the archosaurs flourished, filling niches left open by vanished creatures.